One example of an EMAS system or compressible vehicle arresting system comprises material placed at the end of a runway that will predictably and reliably crush (or otherwise deform) under the weight of an aircraft traveling off the end of the runway. The resistance provided by the low-strength material decelerates the aircraft and brings it to a stop within the confines of the overrun area. An object of the EMAS is to fail in a predictable, specified manner, thereby providing controlled, predictable resistive force as the vehicle deforms the EMAS system. An EMAS is thus generally compressible, deformable, crushable, or otherwise able to be compressed or deformed or crushed upon appropriate impact. EMAS is now part of the U.S. airport design standards and is described in FAA Advisory Circular 150/5220-22A “Engineered Materials Arresting Systems (EMAS) for Aircraft Overruns” dated Sep. 30, 2005. EMAS and Runway Safety Area planning are guided by FAA Orders 5200.8 and 5200.9. Alternatively, an EMAS material or compressible (or deformable) vehicle arresting system may be placed on or in a roadway or pedestrian walkway (or elsewhere), for example, for purposes of decelerating vehicles or objects other than aircraft.
The design and manufacturing of EMAS must meet all specified requirements in FAA Advisory Circular 150/5220-22A. Materials of certain strengths are selected to optimize EMAS performance for a specific fleet mix operating on a specific runway. The lifecycle cost calculations from FAA Order 5200.9 assume that EMAS may require replacement at a certain time. In order to determine that installed EMAS systems have maintained designed vehicle arresting capability, a field strength test device and test method needs to be developed to measure the strength of installed EMAS over time.
U.S. Pat. No. 5,789,681 describes one example of a test apparatus and test method for EMAS material. This patent also defines the Compressive Gradient Strength (CGS) standard, which has been used in-house to control material strength in production. However, this patented in-house test method cannot be directly applied to field strength testing of installed EMAS systems at least because the test apparatus is not portable. This system tests an arresting material test section that is positioned on a bearing block. A load is then applied to the test section (using a hydraulic system that controls a shaft with a test probe head) at a relatively fast constant speed with force measurement occurring continuously or at small increments of displacement as the test probe head moves through the sample. However, if one wishes to test an EMAS system that has already been installed, removing one or more portions of the material from the system and transporting those portions back to the laboratory for testing is impractical and unreliable. Examples of potential problems are that the material may be cracked during removal of the test piece, or the entire system may be compromised from the removal of the testing piece, both causing problems with the testing process. Removal of a test piece in some cases conceivably could require that the entire EMAS bed be placed out of service, potentially precluding use of the associated runway for an extended period.
Embodiments of the invention described herein thus provide a strength test device and method that can be easily implemented in the field, on an existing and currently-installed EMAS (i.e. in situ). The desired portable test apparatus should take readings for resistive load and penetration depth. The measured resistive load can be converted into CGS. The penetration depth in the material can be measured using different types of distance measurement devices.
Although some off-the-shelf soil penetrometers are capable of taking both resistive load and distance measurements, they cannot be directly applied to field strength testing of EMAS materials with their current designs. These penetrometers were designed mostly for soil compaction study. For example, the American Society of Agricultural Engineers (ASAE) and the American Society for Testing and Materials (ASTM) require the use of punch heads with cone shapes, which are particularly designed for soil testing, but they cannot be used for EMAS testing due to the unique properties of EMAS materials. Accordingly, embodiments of this invention provide a portable system and testing method for testing various features of currently-installed EMAS systems.